This description relates to subsea boosting, more particularly, to systems and methods for subsea boosting in a high-voltage direct current (HVDC) transmission and distribution system.
As oil and gas fields in shallow waters diminish, producers are tapping offshore fields in deeper waters with oil installations that operate far below the surface of the sea. The typical equipment for such subsea oil recovery and production include gas compressors and various pumps for multiple functions. Electric variable speed drive (VSD) and motor systems are one way to power such equipment directly under the deep water. Therefore, the delivery of electric power from a remote onshore utility grid or power generation is important to secure a reliable production and processing of oil and gas in subsea locations. Typically, the transmission power requirement is up to several hundred megawatts for medium to large oil/gas fields.
Alternating current (AC) transmission and distribution systems are sometimes used for delivery of power to subsea locations. Such systems typically deliver AC power from a platform or terrestrial location to a large subsea transformer through a large power cable. Power is transferred from the subsea transformer to subsea AC switchgear through another power cable. The subsea AC switchgear feeds AC power to one or more subsea VSDs via yet another cable. The VSDs each provide variable AC power to electric motors via a power cable. The connections between components in subsea AC distribution systems typically require wet mateable connectors, which are significantly more expensive than dry mateable connectors. In addition, the size of components in subsea boosting systems has generally increased over time. Some known systems utilize three to five megavolt-ampere (MVA) pumps, each of which may weigh more than ten tons. Other components in known subsea boosting systems and/or AC transmission and distribution systems are also very large and/or heavy. Moreover AC transmission and distribution systems face technical challenges, which become more significant when transmission distance is in excess of fifty kilometers. For example, the significant reactive power drawn from the distributed subsea cable capacitors constrains the power delivery capability as well as increases the system cost.